Method and Apparatus for Ground Improvement Using Compacted Aggregate Columns

ABSTRACT

An apparatus and method for forming compact aggregate columns. The apparatus includes an aggregate materials hopper; a hollow mandrel adapted to be driven into the ground; a plurality of rubber bearing isolators disposed between the mandrel and the hopper for reducing transmission of vibratory energy between the mandrel and the hopper, and a rubber seal encircling and moulded to the outer circumference of the mandrel for preventing aggregate leakage from the hopper; flow control means comprising a stone gate or hinged tip convertible between an open position and a closed position for controlling aggregate flow, one or more collars encircling the mandrel disposed along the length of the mandrel, each collar having an outer circumference greater than the mandrel circumference; a vibratory hammer attached to a vehicle for inserting and removing the mandrel into the ground; and a monitoring and control system in the cab of the vehicle.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to ground improvement. In particular, the present invention relates to methods and apparatus for ground improvement using compacted aggregate columns.

BACKGROUND OF THE INVENTION

It is known to provide methods and apparatus for forming compact aggregate columns in ground improvement efforts. There are a variety of methods and equipment in common use which use compacted gravel as a means of improving the density and strengths of soils commonly called “ground improvement”. Some of these methods include the use of driven gravel columns using the expanded base (Franki Pile) method, and vibro-flotation with or without air, water, or the introduction of aggregates.

It would be desirable to improve such systems by controlling the aggregate flow through the tube, increasing efficiency by concentrating the vibratory energy, and improving the densification of the surrounding soil. The present invention meets all of these objectives.

SUMMARY OF THE INVENTION

There is provided an apparatus for forming compact aggregate columns, the apparatus comprising a materials hopper having a top opening and a bottom opening; a hollow mandrel adapted to be driven into the ground, its upper end passing through the bottom opening in the hopper, and an aggregate receiving opening; connection means between the hopper and the mandrel; flow control means near the upper end of the mandrel, for controlling the flow of aggregate from the hopper into the mandrel; soil densification means disposed along the length of the mandrel; a vibratory hammer for inserting and removing the mandrel into the ground; and monitoring and control means. The mandrel may have an enlarged bottom section.

The connection means may be one or more rubber bearing isolators disposed between the mandrel and the hopper, and a rubber seal between the mandrel and the hopper. Preferably, there are 4 to 8 rubber bearing isolators which reduce vibratory energy transmission between the mandrel and the hopper. The rubber seal may encircle the mandrel and is moulded to the mandrel.

The flow control means may be a hinged tip located at the bottom of the mandrel, convertible between a closed position to retain aggregate in the mandrel during driving of the mandrel into the ground, and an open position to allow aggregate to flow from the mandrel during raising of the mandrel.

Alternatively, the flow control means may be a stone gate convertible between an open position to allow aggregate flow from the hopper to the mandrel, and a closed position to prevent aggregate flow from the hopper to the mandrel.

The soil densification means may be one or more collars encircling the mandrel, each collar having an outer circumference greater than the mandrel circumference. As the mandrel is driven into the ground, the collars increase the densification of the soil in their vicinity. The collars may be spaced at intervals along the length of the mandrel, preferably at 5 foot intervals.

The vibratory hammer used to drive and retract the mandrel may be attached to a vehicle, and the system may be monitored and controlled from monitors and controls located in the cab of the vehicle.

There is also provided a method for forming compact aggregate columns, the method comprising the steps of filling a hollow mandrel with aggregate from a hopper above the mandrel through an opening in the side of the mandrel; closing a stone gate near the upper end of the mandrel to prevent aggregate from rising in the mandrel; driving the mandrel into the ground with a vibratory hammer, wherein driving the apparatus into the ground displaces the soil outwardly and downwardly from the mandrel to create a hole extending downwardly from the ground surface, and compacts aggregate present in the hole into an aggregate column; withdrawing the mandrel, thereby allowing aggregate to exit the mandrel into the hole; opening the stone gate to allow more aggregate to fill the mandrel; and repeating the above steps until a compacted aggregate column of a desired length is achieved.

BRIEF DESCRIPTION OF THE DRAWINGS

A detailed description of the preferred embodiments is provided by way of example only and with reference to the following drawings, in which:

FIG. 1 is a plan view of the apparatus of the present invention;

FIG. 2 is a plan view of the lower end of the mandrel of the assembly, according to one embodiment of the invention;

FIG. 3 is a plan view of the lower end of the mandrel of the assembly, according to another embodiment of the invention;

FIG. 4 is a front view of the hopper of the assembly, according to the invention;

FIG. 5 is a side view of the hopper of the assembly, according to the invention;

FIG. 6 is a top view of the hopper of the assembly, according to the invention;

FIG. 7 is a side view of the assembly below the hopper depicting the connection between the hopper and the mandrel, and the stone gate;

FIG. 8A is a top view of the top of the mandrel;

FIG. 8B is a side view of the top of the mandrel;

FIG. 9 is a cross sectional view of the upper end of the apparatus of the invention, showing the stone gate in an open position;

FIG. 10A is a top view of the stone gate in an open position;

FIG. 10B is a cross-sectional view of the stone gate in an open position;

FIG. 11A is a top view of the stone gate in a closed position;

FIG. 11B is an end view of the stone gate in a closed position;

FIG. 11C is a cross-sectional view of the stone gate in a closed position;

FIG. 12 is a side view of a second embodiment of the apparatus of the present invention, having a hinged tip gate;

FIG. 13A is a side view of the hinged tip apparatus of the present invention in the closed position;

FIG. 13B is a front of the hinged tip apparatus of the present invention in the closed position;

FIG. 14A is a side view of the hinged tip apparatus of the present invention in the open position;

FIG. 14B is a front of the hinged tip apparatus of the present invention in the open position;

FIG. 15 is a perspective view of the hinged gate element of the present invention in a closed position; and

FIG. 16 is a perspective view of the hinged gate element of the present invention in an open position.

In the drawings, one embodiment of the invention is illustrated by way of example. It is to be expressly understood that the description and drawings are only for the purpose of illustration and as an aid to understanding, which are not intended as a definition of the limits of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The applicant has developed a method and equipment for the introduction of gravel into the ground with compaction to produce a compacted gravel column.

According to one embodiment, the method involves the use of a mandrel 2, a stone gate 6 to control the flow of gravel and a hopper 8 to introduce the gravel into the mandrel. This assembly is attached to a vibratory hammer (not shown) which is suspended, guided and powered by a track machine base with an adjustable leader at the front of the machine.

According to one embodiment, the apparatus of the present invention comprises a hopper, a mandrel extending downwardly from an opening 10 in the hopper; connection means between the hopper and the mandrel; flow control means at the upper end of the mandrel; soil densification means along the mandrel of the present invention, monitoring and control means; and mandrel insertion and removal means.

The mandrel insertion and removal means preferably comprises a base machine which can be moved into a desired position for driving the mandrel and with capacity to elevate a vibrohammer used to vibrate the mandrel as it is driven into and withdrawn from the soil.

The hopper of the present invention is fillable using a standard loader, a long reach loader or a conveyor where height requires such use.

The connection means for connecting the hopper and the mandrel preferably comprise one or more rubber bearing isolators 12 which surround the mandrel and is designed to reduce the transmission of vibrations between the hopper and the mandrel. The connection means also includes a rubber seal 14 disposed between the hopper and the mandrel to prevent aggregate leakage from the mandrel and to further reduce the transmission of energy to the hopper.

The soil densification means may comprise a plurality of collars 16 welded at regular intervals along the length of the mandrel. Vibration energy is transmitted outwardly from each of these collars into the surrounding soil to increase densification of the surrounding soil.

According to one embodiment, the bottom section of the mandrel may be enlarged in diameter relative to the upper portion of the mandrel. The bottom enlarged section may be approximately 8 inches long, as depicted in FIG. 2. According to another embodiment depicted in FIG. 3, the bottom enlarged section of the mandrel may be six feet in length. Other bottom lengths are also within the scope of the invention.

According to one embodiment of the present invention, the flow control means of the apparatus of the present invention may comprise a stone gate movable between an open position to allow aggregate flow from the hopper into the mandrel, and a closed position to prevent aggregate flow from the hopper into the mandrel. FIG. 7 depicts a closed stone gate 18.

According to a second embodiment of the invention, as depicted in FIGS. 12-16, the flow control means of the apparatus may comprise a hinged tip 20 located at the bottom of the mandrel, which opens and closes to allow aggregate flow out of the bottom of the mandrel extended down from the hopper.

The monitoring and control means of the present invention may comprise hydraulic systems controlled and monitored from the cab of the base machine.

The mandrel insertion and removal means may comprise a base machine that can be moved into a desired position for driving purposes. The base machine is selected to have sufficient capacity to elevate a vibratory hammer used to drive and withdraw the equipment from the ground.

According to the preferred embodiments of the method of the present invention, ground improvement using the present invention is achieved by the following process:

First, the mandrel is driven down using the vibrohammer and base machine. According to the method for use with the hinged tip embodiment, the hinged tip is in a closed position during driving into the soil. The mandrel displaces the soil by a volume equal to the volume of the mandrel (including tip) as it is driven into the soil, thereby increasing soil density. Vibration of the soil by the mandrel as it is being driven down densifies the soil. This may be further enhanced by the addition of collars which welded to the outside of the mandrel at regular intervals, the intervals selected in relation to the soil type and soil response to densification.

Once the mandrel has been driven to its intended depth, the mandrel is raised. According to the stone gate embodiment, the stone gate is opened which allows gravel to flow from the hopper into the mandrel and down to the tip of the mandrel. According to the hinged tip embodiment, raising the mandrel allows the hinged tip to open which allows gravel out of the bottom of the mandrel. As the mandrel is extracted upwards the gravel flows out of the bottom into the cavity produced by the extraction of the mandrel.

The mandrel is extracted a short distance, preferably two to five feet, before being driven back down a distance of preferably two to four feet into the previously deposited gravel. This redriving of the mandrel impacts the gravel and forces it outward to produce a gravel column which is larger in diameter than the mandrel itself. The distance the mandrel is redriven down is a function of the energy required to do so. This energy is measured by hydraulic flow and pressure which is registered and controlled in the operator's cab.

The process of extraction and redriving is continued until the mandrel is completely withdrawn from the ground. Intermittent filling of the gravel hopper with a long reach loader or other equipment takes place as the mandrel is driven and extracted. A gravel column approximately two feet in diameter is produced. Columns of other diameters can be produced by using other mandrel diameters and other hammers.

The apparatus of the present invention improves upon the prior art technology in a variety of ways. The mandrel of the present invention includes collars welded to the mandrel at regular intervals. Depending on the soil type, these collars improve the soil densification capabilities of the mandrel as it is vibrated up and down.

The stone gate of the first embodiment of the present invention is situated just below the hopper. The stone gate may be opened and closed to control the flow of gravel into the mandrel.

The hinged tip of the second embodiment of the present invention is situated at the bottom of the mandrel. The hinged tip may be opened and closed to control the flow of gravel into and out of the mandrel.

One or more rubber bearing isolators may be incorporated between the hopper and the mandrel to significantly reduce the amount of vibration transmitted to the hopper. When filled, the hopper is quite heavy, as much as 16,000 pounds. If the hopper is not isolated from the mandrel, a significant amount of energy would be lost in vibrating the hopper, reducing the energy transmitted to the mandrel.

There is a provided a very sturdy top of mandrel connection point for installation connection of the vibratory clamp. This is an improvement on the bolted plate connection known in the prior art.

There is provided a seal between the hopper and the mandrel which prevents the gravel from leaking out of the mandrel. The seal is made of rubber molded to the outside of the mandrel, which reduces the energy transmission between the hopper and the mandrel. Other seal materials are also possible and within the scope of the invention.

The mandrel of the present invention does not contain any upward flow restrictor mechanism inside the bottom end of the mandrel to prevent gravel from upward movement into the mandrel during driving. The system of the present invention may use a sacrificial plate at the bottom of the mandrel as is widely known in the prior art.

Alternatively, according to the hinged tip embodiment, the present invention may rely on the hinged tip at the bottom end of the mandrel to prevent the upward flow of gravel during the driving process. For the stone gate embodiment, the present invention may rely on the stone gate at the upper end of the mandrel to prevent the upward flow of gravel during the driving process.

It will be appreciated by those skilled in the art that other variations of the preferred embodiment may also be practised without departing from the scope of the invention. 

1. An apparatus for forming compact aggregate columns, the apparatus comprising: an aggregate materials hopper having a top opening and a bottom opening; a hollow mandrel adapted to be driven into the ground, its upper end passing through the bottom opening in the hopper, and having an aggregate receiving opening; connection means between the hopper and the mandrel; flow control means, for controlling the flow of aggregate from the hopper through the mandrel; soil densification means disposed along the length of the mandrel; a vibratory hammer for inserting and removing the mandrel into the ground; and monitoring and control means.
 2. The apparatus of claim 1, wherein the connection means comprises one or more rubber bearing isolators disposed between the mandrel and the hopper, and a rubber seal between the mandrel and the hopper.
 3. The apparatus of claim 2, wherein the one or more rubber bearing isolators comprise 4 isolators.
 4. The apparatus of claim 2, wherein the one or more rubber bearing isolators comprise 8 isolators.
 5. The apparatus of claim 2, wherein the rubber seal encircles and is moulded to the mandrel.
 6. The apparatus of claim 1, wherein the mandrel has an enlarged diameter bottom section and the flow control means comprises a stone gate convertible between an open position to allow aggregate flow from the hopper to the mandrel, and a closed position to prevent aggregate flow from the hopper to the mandrel.
 7. The apparatus of claim 1, wherein the flow control means comprises a hinged tip connected to the bottom of the mandrel and convertible between an open position to allow aggregate flow from the bottom of the mandrel, and a closed position to prevent aggregate flow from the bottom of the mandrel.
 8. The apparatus of claim 1, wherein the soil densification means comprises one or more collars encircling the mandrel, each collar having an outer circumference greater than the mandrel circumference.
 9. The apparatus of claim 8, wherein the one or more collars are disposed at spaced intervals along the length of the mandrel.
 10. The apparatus of claim 9, wherein the one or more collars are disposed at intervals of 5 feet along the length of the mandrel.
 11. The apparatus of claim 1, wherein the vibratory hammer is attached to a vehicle.
 12. The apparatus of claim 11, wherein the monitoring and control means includes hydraulic systems monitored and controlled from the cab of the vehicle.
 13. An apparatus for forming compact aggregate columns, the apparatus comprising: a materials hopper having a top opening and a bottom opening; a hollow mandrel adapted to be driven into the ground, its upper end passing through the bottom opening in the hopper, and having an enlarged diameter bottom section and an aggregate receiving opening; between 4 and 8 rubber bearing isolators disposed between the mandrel and the hopper, and a rubber seal encircling and moulded to the outer circumference of the mandrel; a stone gate convertible between an open position to allow aggregate flow from the hopper to the mandrel, and a closed position to prevent aggregate flow from the hopper to the mandrel; one or more collars encircling the mandrel disposed at spaced intervals along the length of the mandrel, each collar having an outer circumference greater than the mandrel circumference; a vibratory hammer attached to a vehicle for inserting and removing the mandrel into the ground; and a monitoring and control system in the cab of the vehicle.
 14. An apparatus for forming compact aggregate columns, the apparatus comprising: a materials hopper having a top opening and a bottom opening; a hollow mandrel adapted to be driven into the ground, its upper end passing through the bottom opening in the hopper, and having an aggregate receiving opening; a plurality of rubber bearing isolators disposed between the mandrel and the hopper, and a rubber seal encircling and moulded to the outer circumference of the mandrel; a hinged tip connected to the bottom of the mandrel and convertible between an open position to allow aggregate flow from the bottom of the mandrel, and a closed position to prevent aggregate flow from the bottom of the mandrel; one or more collars encircling the mandrel disposed at spaced intervals along the length of the mandrel, each collar having an outer circumference greater than the mandrel circumference; a vibratory hammer attached to a vehicle for inserting and removing the mandrel into the ground; and a monitoring and control system in the cab of the vehicle.
 15. A method for preparing compacted aggregate columns comprising the steps of: filling a hollow mandrel with aggregate from a hopper above the mandrel through an opening in the side of the mandrel; closing a stone gate near the upper end of the mandrel to prevent aggregate from rising in the mandrel; driving the mandrel into the ground with a vibratory hammer, wherein driving the apparatus into the ground displaces the soil outwardly and downwardly from the mandrel to create a hole extending downwardly from the ground surface, and compacts aggregate present in the hole into an aggregate column; withdrawing the mandrel, thereby allowing aggregate to exit the mandrel into the hole; opening the stone gate to allow more aggregate to fill the mandrel; and repeating the above steps until a compacted aggregate column of a desired length is achieved.
 16. A method for preparing compacted aggregate columns comprising the steps of: filling a hollow mandrel of the type having a hinged tip at its lower end with aggregate from a hopper above the mandrel; driving the mandrel into the ground with a vibratory hammer, wherein driving the apparatus into the ground displaces the soil outwardly and downwardly from the mandrel to create a hole extending downwardly from the ground surface, and compacts aggregate present in the hole into an aggregate column; withdrawing the mandrel, thereby causing opening of the hinged tip to allow aggregate to exit the mandrel into the hole; repeating the above driving and withdrawing steps until a compacted aggregate column of a desired length is achieved; and adding aggregate to the hopper as necessary to maintain the mandrel full of aggregate. 